Effect of Ga- and Zn-modified Al[subscript 2]O[subscript 3] on the properties of Pd/Al[subscript 2]O[subscript 3] catalyst in selective acetylene hydrogenation

Abstract

In this study, the effects of Ga- and Zn-modified Al[subscript 2]O[subscript 3] prepared by sol-gel and solvothermal methods with various Ga/Al and Zn/Al molar ratios (0, 0.1, 0.3, and 0.5) on catalytic performance of alumina supported Pd catalysts for selective hydrogenation of acetylene were investigated. It was found that catalytic performances of the Pd catalyst supported on Ga- and Zn-modified Al[subscript 2]O[subscript 3] prepared by sol-gel method were superior compared to those of Pd-supported on the unmodified Al[subscript 2]O[subscript 3]. Opposite to the catalysts prepared by sol-gel method, all the catalysts prepared by solvothermal method presented lower selectivity of ethylene than that of the unmodified catalyst except Pd/Zn0.1 Al[subscript 2]O[subscript 3] SV that showed higher selectivity. From X-ray diffraction, it was suggested that varying Ga/Al and Zn/Al ratio directly affected the crystalline phases of alumina supports. As revealed by NH[subscript 3]-TPD, modification of Al[subscript 2]O[subscript 3] supports by Ga and Zn could decrease surface acidity of Al[subscript 2]O[subscript 3] so that the catalysts exhibited lower amount of carbonaceous deposits during reaction and less over-hydrogenation of ethylene to ethane. Moreover, differences in the catalyst activity as well as ethylene selectivity of the various Pd/Al[subscript 2]O[subscript 3] catalysts may be due to the differences in (1) the interaction between Pd and the alumina support, (2) the average Pd metal particle size, and (3) acidity of the supports.